Chart of heater power requirements? Extrusion pressure?

Folks,

I'm building a version of the geared extruder to do some experiments on extruder design. Has anyone put together a table of heater power for various plastics vs. extrusion rate? (with a column for extrusion temperature, too :-)

How about pressure (or force on the filament) vs temp and nozzle size?

Thanks,

Mike

See nopheads' blog.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Bob M,

Thanks for the response -- nophead's blog does indeed contain lots of interesting stuff. A great source and thoughtful author.

But could you perhaps point me at some specific posting there that might answer my question? I'm looking for a concise summary. (One of the failings of blogs, wikis, etc., is that unless someone takes the time to summarize the "good stuff", it's hard to find it amidst the crud. And unless you can trust the author (not a problem in this case), finding it is only half the battle.)

TIA,

Mike

As a partial answer to my own question --

Take a look at Wade's geared extruder:
[objects.reprap.org]

In his final test, he's able to exert 16 kg force on a 1.5 mm filament. Converting units, that's 3,200 psi!!!! (By my unit conversion, 1 kg force/(9/4 π mm^2) ~ 200 psi. Let me know if that's in error.) That's an amazing number for the little mechanical assemblies used here. I suspect something will leak or break before this pressure is reached at the nozzle.

Anybody measure the more typical force applied to push a filament into a Mendel, etc., extruder? (An upper bound would be the holding torque of your stepper motor times the shaft radius.)

Mike

PS: Have just requested several professional books on polymer extrusion through interlibrary loan <-- wonderful tool. Some of these books are amazingly expensive, e.g., $300, and not very commonly found. I'll let you know what practical info I can glean from them.

The heater power needed depends mainly on how well insulated your nozzle is. I have always used about a 20W heater and when running at 240C the average power has been between 50% and 80% of that depending on extruder design. The extra to heat the plastic is about 3 watts when extruding 0.5mm filament at 16mm/s:
[hydraraptor.blogspot.com]

There is a table of flow rates and force for various plastics here: [hydraraptor.blogspot.com] but it varies dramatically with the design of the transition zone in the extruder. With a poor design it can reach infinity very easily! I.e. it can jam solid if the transition zone has more than a certain length and coefficient of friction.

There is also a table of how much force various drive mechanisms can produce here:
[hydraraptor.blogspot.com]

These figures are my experience, YMMV. Small differences in extruder design can have a very big effect.

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[www.hydraraptor.blogspot.com]

nophead,

Thanks. Great stuff. Seems like the world of RepRap could well benefit from a topic index into your blogs. (Does that exist already? Am I missing something? :-)

Mike (another experimenter)